a) Field of the Invention
This invention relates to a buckle assembly, and especially to a buckle assembly for a seat belt system arranged for a seat of a vehicle such as an automotive vehicle.
b) Description of the Related Art
Conventionally, a seat in a vehicle such as an automotive vehicle has been provided with a seal belt system. A buckle assembly for the seat belt system is generally provided with a tongue plate arranged on an end of a webbing and a buckle main body for releasably latching the tongue plate. Such buckle assemblies for seat belt systems include, for example, those disclosed in Pouget U.S. Pat. No. 4,182,008 and Clarke et al. U.S. Pat. No. 5,271,129.
A buckle main body of a buckle assembly disclosed in U.S. Pat. No. 4,182,008 is provided with a base, a slider arranged on the base such that the slider is pushed and moved by a tongue plate inserted in the base, a coil spring biasing the slider in a direction in which the tongue plate is pulled out, a latch plate movable to a tongue plate latching position when pushed by the slider, an auxiliary lock member, such as a pin, for retaining the latch plate in a latching state, a coil spring biasing the auxiliary lock member in the direction in which the tongue plate is pulled out, and a release button for releasing the latching state.
On the other hand, a buckle main body of a buckle assembly disclosed in U.S. Pat. No. 5,271,129 is provided with a base, a slider arranged on the base such that the slider is pushed and moved by a tongue plate inserted into the buckle assembly, a coil spring biasing the slider in a direction in which the tongue plate is pulled out, a latch plate movable to a tongue plate latching position when pushed by the slider, a block member slidable on the latch plate, a lock control member supported on the base, a coil spring biasing the lock control member, and a release button for releasing the latching state.
However, the buckle assembly disclosed in U.S. Pat. No. 4,182,008 involves a potential problem of occurrence of a so-called "false-latching phenomenon" in that, when performing a change-over of the latch plate between the latching position and an unlatching position by operating the release button, the auxiliary lock member may be held down by the base into a pinched state under the biasing force of the coil spring biasing the auxiliary lock member and the biasing force of the coil spring biasing the slider and may hence become stationary at an intermediate position.
The buckle assembly disclosed in U.S. Pat. No. 5,271,129 causes the block member, which plays the role of the auxiliary lock member, to move along a substantially L-shaped path, thereby making it more difficult to induce balancing of forces at an intermediate position where the latch plate may become stationary. However, this block member is also a force-bearing member. Formation of the block member with a metal to provide it with sufficient strength is accompanied by a problem of higher cost. If the block member is formed of a resin with a view to reducing its production cost, a potential problem then arises in that the reliability on its strength may be adversely affected when a high load or high impact is applied to the buckle assembly.
Buckle assemblies of another type include, for example, those disclosed in Barnes et al. U.S. Pat. No. 4,899,424 and Doty et al. U.S. Pat. No. 4,562,625.
A buckle assembly disclosed in U.S. Pat. No. 4,899,414 is provided with a base, a slider arranged on the base such that the slider is pushed and moved by a tongue plate inserted into the buckle assembly, a coil spring biasing the slider in a direction in which the tongue plate is pulled out, a latch plate movable to a tongue plate latching position when pushed by the slider, a lock member as a block member for retaining the latch plate in a latching state, a coil spring biasing the lock member in the direction in which the tongue plate is pulled out, and a release button equipped with a tilted surface for releasing the latching state and also for causing the lock member to move to a non-locking position.
Further, a buckle assembly disclosed in U.S. Pat. No. 4,562,625 is provided with a base, a slider arranged on the base such that the slider is pushed and moved by a tongue plate inserted into the buckle assembly, a lock member connected with the slider by an arm member and movable between a locking position and a non-locking position, a coil spring biasing the arm member, a latch plate movable to a latching position upon movement of the arm member and lock member when pressed by the slider, and a release button equipped with a tilted surface for causing the lock member to move to the non-locking position.
In each of the buckle assemblies disclosed in these patents, upon performing a change-over of the latch plate between the latching position and the unlatching position by operating the release button, a component of force is caused to occur in a non-locking direction (releasing direction) of the lock member by causing the lock member to move to the non-locking position with the tilted surface formed on the release button.
The buckle assemblies disclosed in of U.S. Pat. Nos. 4,899,424 and 4,562,625, however, may each develop an increase in the coefficient of friction between the tilted surface formed on the release button and the lock member or sticking between the above-described tilted surface and the lock member, for example, due to a foreign matter penetrated inside the buckle assembly. If such a situation arises, there is a potential problem that the division of force in the non-locking (release) direction by the tilted surface alone of the release button may become insufficient, leading to a potential risk that the tongue plate can be hardly released even when the release button is pressed.